1. Field of the Invention
The invention relates to a method for improving the concentricity of an automobile tire in which its bead is subjected to post-treatment for improving its concentricity after vulcanization.
2. Discussion of Background Information
German Patent No. 458 554 discloses a process for balancing tube-like hollow shafts made of metal, in which, at the locations where an unevenness in mass distribution causes an excessively large centrifugal force to arise, small inward dents of the shaft wall, i.e., dells, are produced.
In 1972, the German utility model G 72 28 584.8 disclosed a device for monitoring the bead characteristics of motor vehicle tires. In this connection, the tire bead is moved onto a drum, which is apparently divided into segments, and the segments are moved radially apart. The reaction forces exerted on the segments in this process are measured.
In 1998, DE-OS 196 43 762 A1 disclosed a further development of the above-mentioned device in which the conicity of the segments that can be moved radially apart is adapted to the conicity of the rim seat surfaces for the purpose of evening out the compression. Here, it is discussed for the first time that bead rubber can flow plastically under extreme compression. By reducing the maximum compression, this source of errors should be stopped.
DE-PS 24 55 279 C2 discloses a process for balancing a pneumatic wheel by means of plastically deforming the rim.
It is known from DE-OS 27 15 111, in order to reduce tire unbalance, to expose completely vulcanized tires to such a post-treatment that additional rubber is applied or removed on the axially inner side of the bead.
It is known from EP 0 405 297 to locally shift the bead in an analogous manner as in the previously mentioned reference using a detachably mounted disk of adjusted thickness over the circumference in such a way that the bead creates a more even radial force in the tread zone at a given tire deflection.
DE-OS 43 09 513 A1 discloses various processes for improving tire concentricity of a pneumatic wheel, among those a plastic deformation of the rim.
It is known from DE 43 39 775 A1 to remove, preferably to grind down, some rubber from the radially inward pointing bead surface on those locations, i.e., phase positions, where the tire the tire creates too large a radial force or has too large a tread radius. This appears to us to be the nearest prior art.
U.S. Pat. Nos. 3,550,442; 3,719,813; 3,862,570; 4,016,020, and 4,414,843, as well as Japanese Application No. 61-195 809 also relate to the correction of tire unevenness.
The retroactive application of rubber, as known from the above mentioned DE-OS 27 15 111, causes difficulties in practice because the green tires are generally coated with a separation agent before vulcanization. At the locations where rubber is to be applied retroactively and be attached firmly by means of vulcanization, this separation agent must be removed thoroughly and the seam surfaces must be roughened; both processes are several times more expensive than removing rubber, regardless of where from.
A disadvantage of the method according to DE 43 39 775 A1 is that this type of fault compensation is practically irreversible because, as previously explained, the retroactive (re)application of rubber is very expensive; thus it follows that generally the first correction is also the last possibility. Therefore, there must be a very high degree of certainty as to how much must be removed at which location before the irreversible reduction is executed. According to prior experience, good results are achieved herewith only when each treated tire has previously been individually measured, even when the tires of the same batch contain a common systematic defect in addition to the random individual defects.
Another disadvantage of the above mentioned method is that the rubber abrasion causes soiling of the working areas.
Although EP 0 405 297, which has already been cited, avoids these two disadvantages, it is unfavorable for all tire-mounting enterprises, i.e., the automobile manufacturers and the tire dealers, because it requires the handling of two additional components per wheel.
The invention avoids the disadvantages mentioned herein.
By way of background, the inventors realized that the bead should remain the point of intervention because only by avoiding the tread as a point of intervention will the performance and the useful life of the tire remain unchanged by the correcting measure. They also realized that the problem they were facing could not be solved within the standard ways of thinking; after all, if no additional part is to be used, grinding is to be avoided due to its irreversibility, and its application is decidedly too expensive, no other options seem available at first.
The inventors broke into this seemingly hopeless situation of contradicting goals with their idea of attaining the object by plastically reshaping the bead during post-treatment, at least in certain areas. This is based on the surprising recognition that many rubber mixtures can be reshaped quasi-thermoplastically when a sufficiently high pressure, a sufficiently high temperature, and a sufficiently long period of influence are used. This is surprising insofar as vulcanized rubber mixtures are considered elastomers, see, e.g., DIN 7724. Here it is stated: xe2x80x9cElastomers, also called vulcanized materials or rubber, have a glass transition temperature Tg of less than 0xc2x0 C. and have no flow range above their operating temperature range up to their dissolution.xe2x80x9d In the report on the conference xe2x80x9cElastomeric Sheets in Flat Roof Constructionxe2x80x9d on Mar. 24, 1981 in Frankfurt/Main, printed in the magazine xe2x80x9cKautschuk+Gummixc2x7Kunststoffe, vol. 34, No. 11/81, pages 927 through 937 it is written on page 931, right column, from line 4 on:
xe2x80x9cElastomers are rubber elastic polymer materials which can no longer be molded thermoelastically, therefore, have no flow range. This is now accomplished by the vulcanization process in which the macro-molecules are interlinked via chemical cross-linking so that they can no longer shift in relation to one another, i.e., they cannot flow.xe2x80x9d
The quasi-thermoplastic flow created according to the present invention proceeds considerably slower than in known thermoplasts and known thermoplastic elastomers. The quasi-thermoplastic flow seems to be not a pure physical gliding-by of chained molecules, but rather a dissolution of highly stressed sulfur bridges and a reconstruction of less stressed sulfur bridges, therefore a remodeling of sulfur bridges:
If the sulfur bridge that is stressed the most and thus contains the most energy is replaced by one of lower stress, then all the other sulfur bridges are stressed more by a small amount. The formerly second most stressed sulfur bridge surrenders also to the additional stress and replaces itself by a less stressed sulfur bridge while releasing energy, and so on. The suggested, but not completely proven, leap of the sulfur bridge connector from one anchor atom of the polymer atom and/or the filler atom to another anchor atom would therefore be in the end a mechanically induced chemical process.
Besides mechanical tension, the course and the result of this chemical process is also influenced by the process temperature and the time available for the process. An increase of the process temperature and/or of the process duration enables the achievement of the same lasting change of measurement by reshaping using a lesser mechanical stress; the reduction of the necessary mechanical stress at an increase of temperature and/or an increase in duration can only be depicted as a linear function in a very small temperature range, if at all.
Even when, with reduced mechanical stress and accordingly higher temperature and/or process duration, the same lasting change of measurement is achieved, the results are not identical because the hardness of the final product is also essential; an increase in process temperature and/or in process duration results not only in the above mentioned and welcome shifting of the sulfur bridges from former to newly found anchor atoms but also in a more frequent breaking, not only of sulfur bridges at the anchor atoms, but also of the sulfur bridges that have become less stable, so that more and shorter sulfur bridges are present after treatment, which effects a greater hardness of the final product.
Therefore, in order to maintain a sufficient degree of softness in the treated bead, excessive processing temperature must be avoided as well as excessive processing duration. The latter must also be avoided due to economic reasons, since the return on the invested capital must not be permitted to be reduced too much by long production times. An advantageous adjustment of the parameters: stress, temperature, and time is provided for by the invention.
It has been proven useful for performing of the process when the rubber mixture contains at least 10 times as much sulfur as is actually used for the formation of the sulfur bridges according to the selected vulcanization data, such as duration of the vulcanization, vulcanization temperature, selection and dosage of activators, as well as selection and dosage of inhibitors in the vulcanizing material; the explanation for this seems to be that, without a sufficient surplus of sulfur in the mixture, the replacement of the highest stressed bridge by a similarly long, yet less stressed sulfur bridge becomes too improbable because the migration paths of some of the sulfur atoms required for this becomes too long; with too small a supply of sulfur, two shorter sulfur bridges, which integrate sulfur atoms from a smaller area and thus require only shorter migration paths, tend to form as the replacement for one long overstressed sulfur bridge. An insufficient sulfur surplus thus acts similarly to an excessive process temperature, i.e., hardens excessively. An especially good quasi-thermoelastic reaction under the influence of heavy pressure is achieved with bead rubber mixtures that contain 30 to 90 times the amount of sulfur that formed the actual sulfur bridges in the vulcanized material.
When the brake of a wheel is used, with the brake usually being positioned in immediate proximity to the rim, the rim is heated considerably which leads to an increase in the diameter of its seating and thus to an increase in compression. In order to maintain the minimum compression even after cooling down of the rim which is necessary to secure the tire against torsion on the rim during force transmission in the longitudinal direction and against its separation at low air pressure the rubber of the bead must elastically expand sufficiently radially inward again after the rim has cooled down.
In order to achieve this certainty, only rubber mixtures whose set is extremely low must be used in the bead area; therefore, bead mixtures are xe2x80x9cbredxe2x80x9d for the goal of being highly elastic. Due to this, the practical realization of the suggested solution seemed improbable, since a lasting deformation should be achieved.
The problem of the temperature-dependent change in diameter becomes even more severe when one considers the variations of the outside temperatures when a material is used for the rims with a different expansion coefficient in relation to the modulus of elasticity than for the stability carrier of the bead core, thus in particular, in the use of rims made of alloys of aluminum and/or magnesium. As is well known, the linear expansion coefficient for iron is 1.2xc3x9710xe2x88x925, the modulus of elasticity 2.1xc3x97105 N/mm2, however the expansion coefficient for aluminum is 2.2xc3x9710xe2x88x925, the modulus of elasticity 0.65xc3x97105 N/mm2. With increasing outside temperature and an even temperature of the rim and tire bead, therefore, the pressure at the foot of the tire is reduced when an aluminum rim and a steel bead core are used.
To summarize the discussion of the variations in diameters, it has always been important (and continues to be so in the invention) that the residual deformation caused by the operating conditions remains extremely small. The tensions or surface pressures used in the deformation according to the invention are significantly greater than the ones occurring during intended operating conditions, however. And under the influence of this higher mechanical stress, the sulfur-vulcanized rubber reacts quite differently, as discovered by the inventors and described in the paragraphs above. This different material behavior used for the process according to the invention could not be anticipated from extrapolation from the prior known force-deformation behavior.
In contrast to the reaction of thermoplasts and the thermoplastic elastomers, the plasticity realized by the use of significantly higher mechanical tensions is not completely reversible; a single reversion of a previously achieved xe2x80x9cquasi-thermoplasticxe2x80x9d deformation according to the invention by a second quasi-thermoplastic deformation in the opposite direction deposits a small hardening at the place of treatment. The repeated performance of such a plastic cycle of deformation results finally in brittle fracture; therefore the rubber in the taught area of tension resembles the plasticity reaction of metals rather than that of thermoplastic polymers, referred to here as thermoplasts for short.
A particular attraction of the solution according to the invention is the fact that no material needs to be removed from the bead, or, in fact, from the tire as a whole, during post-treatment, and this is preferably not done.
According to one aspect of the invention, the location(s) in which a radial quantity of the tire exceeds the threshold value are first determined in a manner that is known per se. As the radial quantity (as being meant throughout the entire application), it is preferable to use the radial force of the tire, which has first been measured as a function of the angle of rotation in one track, in this case, approximately centered, or in several axially distributed tracks. However, it is also possible to use the radius of the tire itself as the radial quantity; variations in the length of the cord from bead to bead are indicated just as well in this manner, although variations in the stiffness such as occur in the areas of overlapping, for instance, are indicated less accurately.
Then, at least at the location in which the radial quantity of the tire exceeds the threshold value and is the largest, preferably in all locations in which the radial quantity exceeds the threshold value by being too large, the radial quantity of the tire is reduced by bringing the bead core closer to the bead seat surface that spans in an essentially axial manner.
Locally bringing the bead core closer to the approximately axial bead seat surface occurs in a practical manner by deforming the bead by regions according to the invention using the local influence of a force component pressing radially from the inside toward the radial outside against the bead seat surface that extends essentially axially and by the influence of heat. This deforming therefore depends on the cooperation of force and heat.
At least one of the two cooperating components of force and heat must be locally differentiated in such a way that it influences only the location(s) to be deformed; according to the invention, the force is locally differentiated, which, according to previous experiments, is easier to embody than the locally different application of heat according to the invention, which is also possible, however. Additionally, it is certainly also possible to administer both force and heat in a locally differentiated manner, i.e., not evenly over the entire bead circumference.
As noted herein, the location(s) in which the radial quantity of the tires crosses a threshold value is (are) determined in a manner that is known per se, although in this case it falls below the threshold. Then, at least at the location in which the radial quantity of the tire falls below the threshold value and is the smallest, preferably in all locations in which the radial quantity falls below the threshold value by being too small, the radial quantity of the tire is increased.
Here, the radial quantity is increased by bringing the bead core further away from the bead seat surface that extends essentially axially.
The local enlargement of distance between the bead core and the approximately axial bead seat surface occurs in a practical manner by way of a localized deformation of the bead according to the invention by a local influence of a force component that presses the bead area to be processed axially inward against its essentially radially extending edges and by the influence of heat. Here again, the cooperation of heat and force are determining factors. As already explained herein, the local increase in distance is also possible by way of local differentiation of heat instead of force, or in addition thereto.
This makes possible for the first time an enlargement of the distance without the necessity of additional parts and/or connecting operations such as gluing, and although reductions in distance have been possible before without additional parts and/or connecting operations, they were only possible by grinding, therefore by loss of material, which adversely influences the balance of the tire and is irreversible.
The enlargement of the distance according to the invention, enables, compared with any reduction of distance, whether compared to reduction according to the invention or conventional reduction by grinding, the compensation of more serious defects because movable or removable volume is influenced from two sides, i.e., both axial sides, and not only from one side, the radial inner side.
The invention provides appropriate measurements for achieving a reduction in distance and teaches appropriate measurements for achieving an increase in distance. In accordance therewith, the force component pressing radially outwardly or axially inwardly should be between 50 and 150 N per mm length of circumference of the sector of the bead surface or bead surfaces, extending essentially axially or radially, in which the plastic reshaping of the bead is intended to occur, and the heat should be, at least in the area of the bead, between 100xc2x0 C. and 230xc2x0 C., preferably between 160xc2x0 C. and 180xc2x0 C., for a duration of the combined influence of force and heat between 10 minutes and 45 minutes.
A variant of the locally differing application of heat according to the invention in performing the correction method according to the invention is the locally differing cooling closely following or immediately after the vulcanizing, i.e., at a time when the tire is still hot. Thus, in this variant, no additional heat is introduced into the tire but sections in which the bead shall not be deformed are cooled; the sections still to be deformed are not cooled or at least are cooled less. On the contrary, it can be useful to surround the areas of the beads to be deformed with heat insulating mechanisms.
The utilization of the residual heat of vulcanization in the tire is certainly also possible in non-local differentiation of the heat, with only locally differentiated deforming force; here it can be recommended to surround the whole tire bead with heat insulation.
The improved concentricity according to the invention is less suitable for correcting short-wavelength eccentricity, but it is very suitable for correcting long-wavelength disruptions; a correction seems possible up to the sixth harmonic in which a local differentiation in force seems to allow shorter-wavelength corrections than a local differentiation in heat. Taking previous economically limiting conditions into consideration, the process according to the invention is only practical to use for the correction of first, second, and third harmonics of the periodic function that describes the radial quantity over the angle of rotation. The correction of the first harmonic is particularly easy.
According to the invention, it is advisable first to determine a radial quantity of the tire, preferably its radial force, over at least one full rotation as a function of the angle of rotation of the wheel and then to perform an extensive enough Fourier analysis that at least the firstxe2x80x94preferably the first, second, and thirdxe2x80x94harmonic of this function is determined.
After the data acquisition, it must be decided if the maxima of the filtered harmonics shall be reduced or if the minima shall be increased or if reducing of the maxima as well as increasing of the minima shall be performed which is particularly recommended for the treatment of the particularly important first harmonic. A mixed proceeding is also possible, e.g., in such a function that an increase of the minimum and a reduction of the maximum is performed in the first harmonic, and in the second harmonic only the two minima are increased and in the third harmonic the three maxima are reduced.
For reducing a maximum according to the invention, the radial quantity of the tire is reduced in the area of the maximum or the maxima of the relevant harmonic, it need not be a maximum of the function of the radial quantity itself, and is reduced in such a way that the bead core is brought closer to the bead seat surface that extends essentially axially.
For increasing a minimum according to the invention the radial quantity of the tire is increased in the area of the minimum or of the minima of the relevant harmonic, it need not be a minimum of the function of the radial quantity itself, and is increased in such a way that the bead core is brought farther away from the bead seat surface that extends essentially axially.
The average wheel load of a lower mid-class car, such as, e.g., VW Golf, Opel Astra, Ford Escort, or Toyota Corolla, is about 2,750 N. At the present state of tire production technology, the typical amplitude of the superimposed first harmonic in a freshly vulcanized tire is between 40 and 125 N, ergo between about 1.5% and 4.5% of the wheel load, depending on the price the purchaser is willing to pay, and thus the care the manufacturer can expend.
Tires are frequently required in which an amplitude of the first harmonic is less than or equal 80 N. Assuming a tire whose amplitude of the first harmonic is 85 N, the change in radial force need not be 85 N but only 5 N; but if the tire is already being examined and treated, it is recommended to aim at a larger change of radial force, preferably by 20% to 60%, in particular preferably by 40%, of the amplitude to be reduced, in this case by about 35 N. In short, the height and the orientation (and of course the phase position as well) of the useful change in radial force to be desired results from a comparison of the actual variation of radial force with the maximum tolerated variation in radial force.
Proceeding from the data determined in this way and from the measurement parameters of claims 5 and/or 8, claim 14 teaches the measurement of the correct duration of influence t of the deforming force and heat according to the following formula:   t  =      c    ⁢                  ∂        R                              (                      T            -                          T              0                                )                2            
Here, Rf is the desired change in radial force to be determined according to the above mentioned criteria, T the predetermined deformation temperature, c a constant dependent on the rubber mixture and T0 the glass transition temperature of the rubber mixture used in the area of the bead.
For the rubber mixtures customary in the bead area of tires the constant xe2x80x9ccxe2x80x9d is between 1.0 and 2.8xc3x9710xe2x88x927 mm2/K2s, for most car tires between 1.6 and 1.8xc3x9710xe2x88x927 mm2/K2s. The pressure and heat treatment of the tire bead performed according to such a calculation leads to surprisingly low and easily reproducible eccentricities.
The inventors were not satisfied with the impression that most variations in radial force within standard tire series seem randomly distributed. They were able to show that the largest part of the eccentricities are presented as systematic flaws in final assembly of all green tires of a batch in such a way that the required seams are each positioned in the same phase position. Therefore, and due to the above described good reproductivity they suggest:
a) that, during the final assembly of all green tires of one batch, the necessary seams are each arranged in the same phase position and
b) that all green tires of this batch in a certain phase position are placed into similar vulcanization forms, preferably the same vulcanization form, and vulcanized,
c) that a representative collective of n tires, where xe2x80x9cnxe2x80x9d preferably equals 8, is removed from this batch,
d) and all tires of this collective are cooled off, preferably below 75xc2x0 C.,
e) whereafter each tire of this collective is pulled onto a measuring rim and a radial quantity (Rxcexc), preferably the radial force, is measured for each tire over the rotational angle (phi), where xe2x80x9cxcexcxe2x80x9d is to run between 1 and xe2x80x9cnxe2x80x9d.
f) whereafter these individually measured function progressions of the radial quantity Rxcexc=fxcexc (phi) are linearly averaged according to their phases to a mean radial quantity of
Rm=fm(phi)=1/nxc3x97[R1+R2+ . . . +R(nxe2x88x921)+Rn],
g) whereafter, dependent upon the mean radial quantity Rm(phi) thus determined, the plastic bead deformation is determined, in the preferred case, according to the invention, and then the plastic bead deformation thus determined is performed on all n tires on this collective,
h) that each tire from this collective is then cooled again, preferably under 75xc2x0 C., is again pulled onto a measuring rim, and the radial quantity (R) is again measured over the angle of rotation (phi), and is compared to predetermined tolerance fields, and,
i) if the predetermined tolerance ranges are adhered to, all of the remaining tires from this batch are treated in this manner, plastically deforming the bead (2).
According to a preferred further development of this process according to the invention, an additional representative collective shall be taken from the batch in the rare case of non-compliance with the predetermined ranges of tolerance
in which the additional collective contains no tires from the first collective
in which the additional collective is treated
after which in case of compliance with the predetermined ranges of tolerance all remaining tires of this batch are treated in the same manner of plastically deforming areas of the bead.
The tires of the first attempt for improving the concentricity are therefore declared to be not representative and excluded; suitably, they are treated individually or are devalued in their quality certification. Since previous test experience has only in very rare occasions proven the first randomly selected collective to be not representative, the economical advantages of the collective tire treatment outweigh the disadvantage of the rarely necessary second treatment or devaluation.
The best and most uniform tire quality is achieved when according to the invention a radial quantity, preferably the radial force, is measured not only in a single measuring track, which then would be positioned in the zenith area of the tire, but measured in two tracks, namely right and left from the center of the tire. In case of deviations of radial quantity, whether in the amount or the position of the phase, both beads of the tire can be plastically deformed separately, but preferably simultaneously. Here, the words xe2x80x9cseparately deformedxe2x80x9d mean not only that the amount of the deformation can be different in both beads but also that the area of the length of the arc(s) in which one of the beads is plastically deformed can differ from the area of the length of the arc(s) in which the other bead is plastically deformed. According to previous test results, deviations in the amount of deformation can be achieved with equal success by a temperature differentiation as well as an appropriate deformation force differentiation; a variation in the phase can also be achieved by a temperature differentiation as well as a deformation force differentiation, however, a deformation force differentiation is easier.
Independent of the question of whether, for the sake of simplicity, both beads are treated in the same manner or differently in order to achieve higher precision, there are two possibilitiesxe2x80x94which can also be combined with one anotherxe2x80x94to achieve a plastic deformation in predetermined locations of the circumference, and not on others:
a) a bead to be treated is exposed to an expansion stress over its entire circumference but receives a temperature above the necessary deformation temperature only in the areas to be deformed (Key word: localization of the temperature) and/or
b) a bead to be treated receives a temperature above the necessary deformation temperature over its entire circumference but only in the areas to be deformed is exposed to expansion forces of such an extent that plastic deformation occurs. (Key word: localization of the deformation force)
For temperature application, particularly easy in case b), it is possible to use the already existing vulcanization heat instead of heating with a separate heat supply. Here, it is useful according to the invention for the tires of a batch, except the tires of the representative collective(s),
by way of a sufficiently short time span between the removal from the vulcanization form and performance of the plastic deformation, at least regionally, and/or
by way of heat insulating materials that at least wrap around the tire beads
the cooling of the tire is braked to the extent that the tires still have a temperature between 100xc2x0 C. and 230xc2x0 C., preferably between 160xc2x0 C. and 180xc2x0 C. at least in the bead area while being pulled onto the device causing the bead deformation without heat energy being supplied to the tire bead.
Such a processing results in an unchanged energy consumption in the production process compared with the prior art. The comparatively high specific heat of rubber and metal and the low heat conductivity of rubber also results in a particularly fast processing, because the short additional time necessary for setting and removing of the heat protection caps offsets the omission of the considerable time of heating that is otherwise necessary.
The localization of the heat application is harder to realize than localization of the force application due to the heat inertia of the heating devices and only one of the two must occur locally (but both may certainly occur locally). The localization of the heat application in relation to the phase position is most easily realized when the heating device is provided in a fixed phase position on the device and the necessary variability of the phase position is achieved by a mounting of the tire to be deformed onto this device at an appropriate phase instead of mounting the tire in a random phase position and adjusting the phase of the heating device. In the latter embodiment, considerable currents had to be switched over variable electric paths which, in the proximity of rubber, can cause electric arcs resulting in charring.
This problem of realizing a localization of the heat influence (i.e., a locally concentrated heat influence, rather than one acting uniformly over the entire circumference) does not exist, when the localization is achieved not by locally concentrating the heat influence but by locally concentrated heat insulation and/or by a locally complementary cooling. The latter is an object of the invention in which the localization of the heat influence in achieved in such a way that before the deforming force is introduced, the areas of the bead to remain generally undeformed are cooled, preferably to a temperature below 75xc2x0 C.
The preceding parts of the description are based upon the awareness that tire unevennesses regardless of their origin can be reduced or even removed retroactively by selective plastic deformation of the bead. Here, the word xe2x80x9cselectivexe2x80x9d includes the idea that the amount and phase position of any unevennesses, preferably of the radial force, first in at least one measuring track, preferably in two measuring tracks, are determined and then a bead deformation calculated from the amount and the phase position is performed.
A statistic comparison of tires post-treated in this way with tires that were not post-treated presented the surprising result that tires post-treated in this way do not show any higher variations in material thickness between the inner radius of the bead core and the inner radius of the bead, but rather lower ones. Originally greater variations had been expected over the circumference since a deformation is impressed. This unexpected fact leads to the suggestion that a considerable part, approximately one third, of the tire unevennesses to be compensated according to the invention are variations of previously mentioned material thickness, also called xe2x80x9cinner coating thickness.xe2x80x9d To this extent, the localized plastic bead deformation mentioned above is therefore not only a process to fight a symptom but rather a process that acts on the chain of causality.
According to the above mentioned awareness, the tire evenness is already improved in the statistic average with a non-selective, yet even, and thus leveling, plastic bead deformation. The word xe2x80x9cevenxe2x80x9d relates here to the distances of the deforming sections; the forces are not even: in the phase positions in which more rubber is situated below the bead core more deforming force is introduced in even distances than in the phase positions in which less rubber is situated below the bead core.
In similar fashion to the even bead enlargementxe2x80x94distancewisexe2x80x94an even reductionxe2x80x94also distancewisexe2x80x94of the clear opening of the beads leads to a leveling of the radial force diagram. This is possible, by even axial compression, also distancewise, by exercising pressure on the generally radially extending surfaces of the bead.
All mentioned developments of the process according to the invention for plastic deformation of the bead after the vulcanizing of the tire show that new devices must be designed for their performance. According to prior knowledge these devices cannot be used for anything else but the performance of these processes.
The first variant of the developments of the invention is purposefully embodied according to the invention in that the tire bead is axially pressed onto a conical calibrating rim at a bead temperature between 100xc2x0 C. and 230xc2x0 C. Thus, the material distribution is leveled in the core area, in particular between the inner circumference of the bead core and the inner circumference of the bead.
The device according to the invention can be modified in such a way that the conical drum widening the bead is not circular in its cross-section, but rather is designed with an out-of-roundness in the first or second or third degree which leads to a device according to another embodiment of the invention.
xe2x80x9cOut-of-roundness in the first degreexe2x80x9d means that the cross-sectional profile in each axial position of the cross-sectional plane does not show a constant radius, represented in polar coordinates, but rather a radius R varying according to a function R=Rm+c sin phi. This leads to an egg-shaped cross-sectional profile.
Out-of-roundness in the second degree means that the cross-sectional profile in each axial position of the cross-sectional plane shows a radius R, represented in polar coordinates, varying according to a function R=Rm+c sin(2 phi). This leads to an elliptical cross-sectional profile.
Likewise, out-of-roundness in the third degree means that the cross-sectional profile has in each axial position of the cross-sectional plane a radius R in polar coordinates varying according to a function R=Rm+c sin(3 phi). This leads to a cross-sectional profile similar to a severely rounded triangle.
Likewise, higher degrees are possible but are generally unimportant; the lowering of the amplitude of the first harmonic is most important.
With a device according to the invention, a higher compression is created between bead core and bead seat surface at the places of the greatest curvature of the drum in the cross-section, i.e., at the maxima of R, than in the places of lesser curvature in the drum cross-section. Therefore, rubber is displaced at least more there, and sometimes only there, and that occurs even when the treated tire bead is not locally but evenly hot between 100xc2x0 C. and 230xc2x0 C. Thus, a process according to the invention can be performed. A localization of the heat influence is possible additionally, for example, by differences in thermal conductivity.
An advantage of a device according to the invention is the potential one-piece construction of the conical drum so that the constructional expense is particularly small and no gaps between sections must be accepted or bridged. However, the sliding motion at the inner bead seat surface is disadvantageous, making lubrication thereof recommended.
For the performance of another variant of the process according to the invention, i.e., with a reduction instead of an enlargement of the clear opening of a bead, instead of a conical calibrating rim or a drum in which all sections are extended an equal distance by an appropriate positive control system, a device of such kind is necessary that has two clamping-jaw like rings per bead which can be moved toward each other and which axially compress the relevant bead core between them. For this only one of the two rings need to be movable and none of the rings need to be divided into sections.
The latter embodiment of the two rings axially movable toward each other, which is not divided into sections, results in a particularly low construction expense and, due to its gap-free and edge free design, a particularly good surface quality in the finished tire bead; a device so embodied is provided herein.
The plastic transformation occurs when the two rings are moved together that each axially compress a bead essentially in the areas in which particularly much material is positioned beside the bead core and consequently particularly little material is underneath the bead core. The equality of distance leads therefore to a leveling of the geometry in the deformation.
The device according to the invention can be modified in such a way that the two rings acting on a bead are not guided toward each other coaxially but rather with an adjustable offset which leads to a device which is suitable for the performance of processes according to the invention.
An xe2x80x9cOffsetxe2x80x9d mechanism is provided by the invention so that the rotational axes of the two rings do meet at a location in the middle of the average distance between the two rings (which is expressed in xe2x80x9cconcentricxe2x80x9d), but they meet only in one point, therefore they do not coincide (which would be expressed in xe2x80x9ccoaxialxe2x80x9d), but are positioned at an adjustable acute angle to one other. If the device were to be allowed to rotate, at least one of the two rings would seem to wobble. The term xe2x80x9cwobblingxe2x80x9d in the features of claim 24 is actually superfluous; it is only listed there because sometimes the terms xe2x80x9cdisaxialxe2x80x9d, xe2x80x9coffsetxe2x80x9d, and xe2x80x9coffsetablexe2x80x9d are not as precisely distinguished in the German language from xe2x80x9ceccentricxe2x80x9d etc., as is actually correct. The combination of the terms concentric and coaxial could also be called xe2x80x9calignedxe2x80x9d.
Although this way of performing the process makes it possible to influence only the first harmonic and not the higher harmonics of the variations in radial force or in radius, the devices required for it are particularly inexpensive, particularly reliable in operation and they result in a prime surface quality which finally is a result of the one-piece construction of the pressure rings.
Universally applicable devices are described below which also permit, in particular, the influencing of higher harmonics but due to their multi-piece construction are more expensive.
In the process variants in which rubber is pressed radially from the inside toward the outside, thus process variants according to claims 3 and/or 4, the multi-piece device also has the shape of a drum. The latter has at least two segments of which at least one must be radially movable; preferably it should have more segments, in particular preferably twelve. Preferably all its segments are radially movable.
Drums with those features are known per se and are used prior for the construction of green tires in the tire industry.
In order to be usable in the process according to the invention, such drums must be able to create considerably larger spreading forces without any damage, namely such as they result after multiplication with the appropriate circumference. The loading stress of the drums necessary for the performance of the process according to the invention is more than 2 times the power of ten above the prior known drums. The dimensions of its spreading mechanism alone separates the new drums discussed here to be created according to the invention considerably from those known in the tire industry.
Insofar as the option of using the vulcanization heat is not utilized, drums for the performance of the process additionally need the ability to heat at least one, preferably all, of its sections according to the invention. Therefore, the section surface designated for the contact and the plastic deforming pressure onto the essentially axially extending bead seat surface or at least one of its sections is heatable to the extent that a temperature between 100xc2x0 C. and 230xc2x0 C., preferably between 160xc2x0 C. and 180xc2x0 C., can be achieved.
If the option of using the vulcanization heat is to be utilized, not a single section needs to be heatable; as described above, such embodiment are preferred in mass production and post-treatment.
Concerning the performance of the process for enabling the embodiment of the process according to the invention such drums are preferred according to the invention in which at least one, preferably all, of its sections can be cooled in such a way that its (their) section surface(s) which is or are designated for the contact and the plastic deforming compression of the essentially axially extending bead seat surface can reach a temperature of below 100xc2x0 C., preferably below 75xc2x0 C.
For the performance of a process analogous to the invention as an equivalent substitute for a conical calibrating rim, the use of such a drum would also be possible, of which all sections are extended an equal distance by an appropriate positive control system. The plastic deformation then occurs essentially in the areas in which particularly much material is situated below the bead core.
Drums that can be extended over their circumference only evenly are useful further for the variants of the process in which the temperature influence occurs locally, either by local heating or by cooling in complementary areas.
Particularly preferred, however, are such embodiments of the drum in which according to the invention the sections can be extruded to different extents. Here, a particularly precise and in almost all cases optimal local distribution (in this application called xe2x80x9clocalizationxe2x80x9d) of the deformation force can be achieved.
For the variant of the process in which rubber is pressed radially inwards from the sides, variants of the process according to the invention, also the multi-piece device has a form that could be called a vice with clamping jaws in the form of a ring. Since only vices with short straight clamping jaws seem to be known, only the general term xe2x80x9cdevicexe2x80x9d is used here.
Such a device has according to the invention at least two rings for the clamping of a tire bead in which at least one of the rings is divided into at least two, preferably twelve sections of which at least one can be moved axially. Preferably all sections of one or both rings are axially movable.
It would be sufficient, in general, if only sections of one of the two rings cooperating for each bead were axially movable and then preferably the sections of the axially inner ring. Specifically, possible steps or ridges somewhat resembling flash at the segment seamsxe2x80x94especially in the case of significantly different extension lengths of neighboring segmentsxe2x80x94are less of a problem on the axially inner side than on the outer side where they could interfere with the flush contact between the rim flange and the tire bead.
In order to avoid steps and ridges, it is also possible, just as in the devices that press radially from the inside toward the outside, to provide a smoothing rubber ring or a smoothing rubber collar over the sections preferably produced from metal so that these comparatively hard sections do not act directly on the bead to be deformed, but only indirectly via the smoothing rubber component.
Especially large displacements of the bead core away from the bead seat surface are possible when the axially opposite sections of both rings can be moved axially toward each other. Here, it is possible to correct only long-wavelength disturbances with a section advance of the axially outer ring, preferably only those of the first harmonic, while acting at shorter wavelengths with the segment advance of the axially inner ring, preferably to provide two maxima, of which one is equiphase to the preferably only maximum in the section advance of the axially outer ring.
Furthermore, it is possible when using two rings of axially advanceable sections that only one of the rings, preferably the axially outer one, has a ridge leveling rubber ring on the side facing the bead to be processed.
In similar fashion to the drums, the vise-like devices for axial bead compression also require the ability to heat at least one, preferably all, of its sections, at least when the option of using the vulcanization heat is not used. Thus, at least one, preferably all, of the sections can be heated in such a way that its or their section surface(s), which is or are provided for contact with and plastic deforming pressure on the surfaces that extend essentially radially, can achieve a temperature between 100xc2x0 C. and 230xc2x0 C., preferably between 160xc2x0 C. and 180xc2x0 C.
However, if the option of utilizing the vulcanization heat is used, not a single section needs to be heatable as already mentioned analogously for the radially pressing drums. As already mentioned in the description of the process features such embodiments are preferred in mass production and post-treatment.
Concerning the performance of a process for facilitating a process embodiment according to the invention, such device embodiments are preferred, in a manner similar to that described herein for drums, in which at least one, preferably all, of its sections can be cooled and whose section surface(s) provided for contact and plastic deforming pressure on the lateral bead surfaces which extend essentially radially can achieve a temperature below 100xc2x0 C., preferably below 75xc2x0 C.
The greatest flexibility in applicationxe2x80x94of course, it also involves the highest construction costxe2x80x94is provided by drums in which each section is adjustable to different temperatures by independent cooling and/or heating.
Like all multi-piece plastic deforming tools, the drums and rings addressed in this application have the problem that ridges can be pressed into the beadxe2x80x94the work piece to be deformedxe2x80x94which are undesirable, in particular very undesirable on the radial inner bead seat surface, where tires for tubeless use as is presently customary achieve the necessary seal to the rim. In another part of this application it was proposed to buffer or bridge these ridges and gaps with rubber collars. The invention provides as an alternative to xe2x80x9cpull backxe2x80x9d the tool sections in the proximity of their borders, i.e., to let the sections run out in the proximity of the border so gently that they no longer exert a sufficient pressure. In the specific example of a drum, this means that the sections movable against each other shall be flattened in their borders, also called seams.
In order to reduce the forces necessary for deformation and in particular to further improve reproducibility of the plastic deformation achieved at the completely vulcanized tire bead, it is recommended according to the invention, to set the bead into vibration, preferably in the ultrasonic range, at least in sections, during plastic deforming post-treatment, in the areas in which the only or the largest deformation is to be achieved. This can be achieved by a high-frequency alternating magnetic field that acts on the bead core containing iron. The impact of the force can therefore occur first by an electric and/or magnetic alternating field first on the bead core and only then be transmitted by it onto the bead rubber to be deformed.
If such a field is applied in a circulating, i.e., rotating fashion, it can also be used simultaneously for inductive heating of the bead which thus results in a heat flow from the bead core to the bead surface.
A localized (=selective) introduction of vibrations, i.e., uneven over the circumference, seems easier to achieve, however, since at least one of the components in contact with the bead vibrates during the plastic deformation.
The invention provides a process for improving a concentricity of a pneumatic vehicle tire having a bead, the process comprising subjecting at least a portion of the bead, after vulcanization, to a plastic deformation post-treatment, wherein the post-treatment improves the concentricity of the tire.
The portion of the bead may be deformed without material being removed during the post-treatment. The subjecting may comprise applying locally an essentially axial force component FR to a seat surface of the portion of the bead, the force component being directed radially outwardly from a radially inwardly position. The subjecting may further comprise locally heating a seat surface of the portion of the bead. The subjecting may comprise locally heating a seat surface of the portion of the bead. The subjecting may comprise applying locally an essentually radial force component FR to a seat surface of the portion of the bead, the force component being directed radially outwards from a radially inwardly position. The subjecting may further comprise locally heating a seat surface of the portion of the bead. The force component FR may be between 50 and 150 N per mm of a circumferential length of a sector of a bead seat surface. The heating may comprise heating at a temperature of between 100xc2x0 C. and 230xc2x0 C. The temperature may be between 160xc2x0 C. and 180xc2x0 C. for between 10 minutes and 45 minutes. The subjecting may comprise locally applying a force component Fa to axially compress the portion of the bead. The force component Fa may be between 50 and 150 N per mm of a circumferential length of a sector of a bead seat surface. The heating may comprise heating an upper portion of the portion of the bead.
The process may further comprise determining at least one location when a radial quantity R of the tire exceeds a threshold value, and reducing the radial quantity R of at least that location when the threshold value is exceeded. The radial quantity R may be a radial force. The reducing may comprise causing a portion of a bead core arranged in the bead to move toward a bead seat surface. The process may further comprise determining at least one location when a radial quantity R of the tire falls below a threshold value, and increasing the radial quantity R of at least that location when the threshold value is exceeded. The radial quantity R may be one of a radial force and a tread radius. The increasing may comprise causing a portion of a bead core arranged in the bead to move away from a bead seat surface. The radial quantity R may be determined over at least one complete turn of the tire and as a function of an angle of rotation of the tire. The radial quantity R may be determined over at least one complete turn of the tire and as a function of an angle of rotation of the tire. At least one of a first, a second, and a third harmonic of the function may be determined using a Fourier analysis. At least one of a first, a second, and a third harmonic of the function may be determined using a Fourier analysis. The quantity R may be reduced when a maximum of at least one of the first harmonic, the second harmonic and the third harmonic is determined. The quantity R may be increased when a minimum of at least one of the first harmonic, the second harmonic and the third harmonic is determined. Each of a maximum of the quantity R the maximum of the first harmonic may be reduced and each of a minimum of the radial quantity R and the minimum of the first harmonic may be increased. Each of a maximum of the quantity R the maximum of the first harmonic may be reduced and each of a minimum of the radial quantity R and the minimum of the first harmonic may be increased.
The portion of the bead may be deformed according to the formula:   t  =      c    ⁢                  ∂        R                              (                      T            -                          T              0                                )                2            
wherein Rf is a desired change in radial force to be determined;
wherein T is a predetermined deformation temperature;
wherein c is a constant which is dependent on a rubber mixture;
wherein To is a glass transition temperature of the rubber mixture used in an area of the bead; and
wherein t is the time required to affect a change in the portion of the bead.
xe2x80x9ccxe2x80x9d may be between 1.0 and 2.8xc3x9710xe2x88x927 mm2/K2s. xe2x80x9ccxe2x80x9d may be between 1.6 and 1.8xc3x9710xe2x88x927 mm2/K2s.
The invention also provides for a process for improving a concentricity of a plurality of pneumatic vehicle tires each having a bead, the process comprising providing a batch of xe2x80x9cnxe2x80x9d number of green tires each having a seam, orienting the seams to have the same phase position, vulcanizing the batch of green tires on at least one vulcanization form, allowing the batch of green tires to cool, measuring each of the green tires to determine a radial quantity R over a rotation angle, determining a mean radial quantity Rm by averaging the radial quantities R according to their phase, determining how much to deform a portion of the bead of at least one green tire using Rm, and subjecting the portion of the bead of the at least one green tire to plastic deformation, wherein the subjecting improves the concentricity of each tire in the batch.
xe2x80x9cnxe2x80x9d may be eight. The radial quantity R may be a radial force. The determining of the mean radial quantity Rm may be based upon the formula:
Rm=fm(phi)=1/nxc3x97(R1+R2+ . . . =R(nxe2x88x921)+Rn),
wherein fm is a radial force over a rotation angle phi;
wherein xe2x80x9cnxe2x80x9d is the number of green tires in the batch; and
wherein R is the radial quantity for each green tire.
The green tires may be processed until each tire in the batch meets a predetermined concentricity tolerance. The cooling may be performed at a temperature under 75xc2x0 C. The at least one green tire may be processed until it meets a predetermined concentricity tolerance, and thereafter all remaining green tires in the batch are processed in the same manner as the at least one green tire.
The invention also provides for a process for improving a concentricity of a pneumatic vehicle tire having two beads, the process comprising subjecting at least a portion of one bead, after vulcanization, to a plastic deformation post-treatment, subjecting at least a portion of another bead, after vulcanization, to a plastic deformation post-treatment, wherein the post-treatment improves the concentricity of the tire. Each subjecting may occur separately. Each of the beads may be subjected to a different amount of plastic deformation post-treatment. The different portions of each of the beads may be subjected to a different amount of plastic deformation post-treatment.
The invention further provides for a process for improving a concentricity of a pneumatic vehicle tire having a bead, the process comprising mounting the tire on a drum which comprises at least one of an internal heating mechanism and internal cooling mechanism, subjecting at least a portion of the bead, after vulcanization, to a plastic deformation post-treatment using the drum, wherein the post-treatment improves the concentricity of the tire.
The invention also contemplates a device for improving concentricity of a pneumatic vehicle tire having a bead, the device comprising a drum having a surface which engages a radially inner bead seat surface of the tire, the drum comprising at least one of an internal heating mechanism and an internal cooling mechanism, the drum being adapted to plastically deform at least a portion of the bead of the tire so as to affect at least one of a first, a second, and a third harmonic, wherein the plastic deformation improves the concentricity of the tire.
The drum may comprise at least two curved segments which are mechanically moveable relative to one another. At least one of the segments may be heated by the internal heating mechanism. At least one of the segments is cooled by the internal cooling mechanism. Each segment may comprise a surface which is adapted to engage a radially inner seat surface of the bead. At least one of the segments may be axially moveable. At least one of the segments may be radially moveable. At least one segment can absorb a radial force equal to a product of 50 N/mm times a circumferential length of the at least one segment. The internal heating mechanism may be capable of heating to a temperature of between 100xc2x0 C. and 230xc2x0 C. The internal heating mechanism may be capable of heating to a temperature of between 160xc2x0 C. and 180xc2x0 C. The internal cooling mechanism may be capable of cooling to a temperature below 100xc2x0 C. The internal cooling mechanism may be capable of cooling to a temperature below 75xc2x0 C. Each segment may be separately movable to different positions. Each segment may be adjusted to a different temperature. The drum may include at least one flattened portion in an area where the segments meet. The drum may be capable of causing the bead to vibrate. The drum may be capable of causing the bead to vibrate in an ultrasonic range. The drum may be adapted to simultaneously plastically deform the portion of the bead and to cause a rubber of the bead to vibrate.